Multivibrator and integrating circuit combination



Oct. 24, 1950 E. Lc. WHITE NULTIVIBRAICR AND INTECRAIINC CIRCUITCOMBINATION Filed April 26, 1946 UHT/07' IN VEN TOR. a Wm 2 Sheets-Sheet1 Oct. 24, 1950 E. L. c. WHITE 2,527,342

MULTIVIBRATOR AND INTEGRATING CIRCUIT COMBINATION Filed April 26, 1946 2Sheets-Sheet 2 www Patented Oct. 24, 1950 MULTIVIBRATCR AND INTEGRATINGi CIRCUIT COMBINATION t Eric Lawrence Casling White, Iver, England,assignor to Electric and Musical Industries,V Limited, aBritish companyl Y Application April 26, 1946, Serial No. 665,030 In Great BritainDecember 18, 1943 Section 1, Public Law 690,- August 8, 1946 Y Patentexpires December 18, 1963 2 Claims. (Cl. Z50-27) This invention relatesto l,electrical Circuit arrangements and more particularly vto circuitarrangements for generating electrical pulses having a predeterminedtime delay with respect to a series of master pulses or for generatingelectrical waveforms such as sawtooth waveforms.

According to the invention there is provided an electrical circuitarrangement comprising an integrating circuit and a 'multivibratorcircuit having two conditions of` equilibrium and coupling means socoupling said circuits that when the voltage or current developed yinsaid integrating circuit reaches a predetermined value, saidmultivibrator circuit changes its condition of equilibrium and causes amodification of the integration of said integrating circuit.

If it is desired to generate pulses havinga predetermined delay withrespect to a master pulse, saidV coupling means may be such that saidintegration is interrupted by the changerof equilibrium of saidmultivibrator circuit and `said inte' grating circuit is restored to apredetermined condition and means may be provided for applying saidmaster pulse to said multivibrator so as to change its condition ofequilibrium to cause said ther means provided for developing saiddelayed pulse when said multivibrator again changes its condition ofequilibrium under the control of said integrating circuit. Y v

If, on the other hand, it is desired to generate oscillations having asawtooth waveform, said coupling means may be such that said integrationis reversed in sense by said change of the condition of equilibriumof'said multivibrator vcirc/uit and means may be provided which when thevoltage or current developed in said integrating circuit during saidintegration in reversed sense reaches a further predetermined value,causes said integration again to be reversed in sense whereby sawtoothvoltage or current oscillations are developed in said integratingcircuit.

If desired, said coupling means may be such that the rate of saidintegration is modified by said change of condition of saidmultivibrator circuit.

In order that the invention may be more clearly understood and readilycarried into effect, examples of the application of the invention tothegeneration of the delayed pulses and to the generation of sawtoothoscillations will now be more fully described with reference to theaccompanying drawings in'whichr Figure 1 'is a circuit diagram of oneembodiment of the invention for producing electrical pulses, f Y

Figure 2 is a circuit diagram of anotherembodiment of the invention,and' Figures `3 and 4 are-circuit `diagrams of two embodiments 'of theinvention for producing sawtooth waves. v'

Figure l illustrates the invention as applied to a circuit for thegeneration of delayed pulses under the control of master pulses. Thecircuit shown comprises an integrating circuit including the valve lassociated with a multivibrator circuit comprising valves 2 and 3. Theintegrating circuit is of the kind described in the specication yofiapplication Serial` No. .592,64l, filedl May 8,

`biased lso* as to render valve l conductingor nony conducting. Whenvalve lfis in the non-conductingstate its anode` rapidly rises to amaximum ,25 integrating circuit to become operative and fur-4 tion of apositive voltage to the grid il, thev'oltage on the anode 'l falls atauniform rate determined by thevalues of resistance 4, capacity .5 andthe v`voltage applied tothe end of resistance i remote from the grid 8fl The multivibrator circuit is of a known type in which two valves 2, 3share a common cathode resistance I0 and are further coupled bymeans ofa resistance Il yconnected betweenfthe anode l2'of one valve 3 andthevcontrol grid|3 of the othervalve 2. Acoupling resistancey ifiv is.-in f cludedin the anode circuit of valve 3 and an inductance coil orother impedance i5, from which an output may be taken, is included intheanode circuit of valve 2. Multivibrator circuits of this kind havetwo stable conditions of equilibrium and can be caused to pass from onevcondition to the other by the application of a suitable bias to thecontrol grid of either valve. Y-

It will be observed that the grid 9 is connected via resistance I6 tothe anode ll2 so that-changes of the voltage of anode l2 arecommunicated to grid 9. Grid 9' is also biased to a suitable voltage byresistance' l1, which is connected to a suitbecomes conducting andlowers the voltage of grid I3 as the voltage of anode 'I continues tofall. Grid 20 of valve 3 is biased via leak resistance 2| which isconnected to the junction point of resistors 23a and 23h connectedacross the source of anode voltage.' The master pulsesV are applied tothe grid 20 via capacity. 22. .Diode 24 is provided to limit themaximum/voltage to which anode 'I rises when valve I is renderednonconducting to a value which can be adjusted as desired. For thispurpose, vthe anode of 'diode 24 is connected to anode 'I and thecathode of diode 24 is connected to an adjustable-tapping 25 onresistance 23a. Thus, when the voltage of. anode I rises to the voltageof tapping 25, the diode 24 becomes conducting and prevents any furtherrise in the voltage of anode 1.

The arrangement operates as follows: Prior to` the application of amaster pulse, the bias conditions of valves 2 and 3 suchv that valve 3is con ducting and valve 2 is non-conducting. Thus, the voltage of anodeI2 and consequently grid 9 are both low, so that valve I is heldnon-conducting and the voltage of anode 1 is equal to the voltage oftaping 25. The master pulse is then applied to grid 20 via condenser` 22with negative polarity and causes valve3 to pass over into thenon-conducting state and the valve 2 to become conducting. The.consequent rise ofA the voltage of anode I2 raises the voltage of grid 9to an extent sufficient to render valve I conducting and to initiatethecharging of condenser 5 and the steady fall of thel voltage ofA anode l.The circuit remains in this state with the voltagek of anode 'I fallingat a uniform rate until the diode I8 eventually becomes conducting andthe voltage-on grid I3, is thereupon loweredto an extent sufcient tocause valve 2 to passover into the non-conducting state and thereby tocausev valve 3'to become conducting again and consequently render valveI non-conducting. Thus, the integrating circuit is automatically resetin readiness for the next master pulse and the current change inimpedance I5 when valve 2 passes from the conducting to thenon-conducting state' can be used to generate the pulse having thedesired delay with respect to the applied master pulse. Impedance I5may, if desired, comprise a time delay, network so as to enable thedelayed pulse to have any required duration in known manner.

It will be appreciated that the time delay of the delayed pulses withrespect to thev master pulses is determined by the time taken for thevoltage of the anode 'l to fall from its Vstarting voltage to thecriticalY voltage of the grid |35 of the multivibrator; With theintegrating circuit shown, dueto the negative feedback provided, thevoltage of Y'gridB is held-substantially constant while the voltage ofthe anode I falls, so that Vthe charging'current flowing into thecapacity 5 will be substantially equal to Ei/Ri, where'Ei is theAvoltage applied to the upper end'offresistance Il and R1 is the valueofresistance `4. Thus, the rate at which the anode potential falls isgiven by Ei/CRi, where C'isthevalue of capacity 5, and if* Ez is thepotential from which`the anode 'I commences to fall and E3 isthepotential of'anode If at which the grid I3 of` the-multivibrator istriggered, thetime delay will be T (Er-E3) in the above formula for T,the Variable shown in the circuit of said Figure 1 being E2, thepotential of theslider 25.

If desired, instead of vproviding an adjustment for setting the value ofE2, E3 may be made adjustable, in which case an A.-C. coupling isprovidedn between the anode of diode I8 and grid I3' and said anode isconnected via a resistance to a point of ajustable potential. As thepotential of anode 1 descends, diode I8 remains non-conducting until itscathode, which is connected to Yanode 'I, falls to a potentialsubstantially equal to the potential impressed on the anode of diode I8by said point of adjustable potential. Diode I8 then becomes conductingand the fall of the potential of anode 'I is thereafter communicated togrid I3 via the A.C. coupling referred to which causes the multivibratorto be triggered, the D.C. bias applied to grid I3 having been chosen tohold grid I3 close to the critical potential. In thiscase, the couplingbetween valves 2 and 3 is preferably arranged between the anode of valve2 and grid 2U so as to avoid the application of back coupling voltagesto grid I3;

In the case of the circuit arrangement of Figure l or variations thereofabove referred to the master pulses may if desired be rectangular and beapplied in the positive sense Vto capacity-22 in which case the valuesof capacity 22 and resistance 2| are chosen so as to differentiate saidmaster pulses and thereby to develop sharp negative impulses on theirltrailing edges. To eliminate thepositive pulses which occur on theloading edges of the master pulses a diode may be inserted between grid20 and. capacity 22 with a polarity such that it is non-conducting forpositive pulses.

It may sometimes be required to provide more than one series of delayedpulses and this may conveniently be done by means of a plurality ofmultivibrators controlled by the same integrating .circuit but havingdifferent critical potentialssothat each multivibrator triggers at adifferent time after the integrating circuit is rendered operative. Insuch cases the integrating circuit is rendered operative and is reset bythe estA delay.

vthe slider 3Il'on theV potentiometer 3l connected An example of acircuit of this kind will now be described with reference to Figure 2,in which elements performing. the same as those shown in'Figure laregivenfthe same reference numerals and elements in a second-mu1tivibratorhaving lsimilar functions to corresponding elements in the rstmultivibrator-are given the same refervence numerals with. the suiiix a.

Acomprising valves 2 and 3.are substantiallyy the -fsame-as-those shownin said Figure 1, the difference being that an A.C; coupling comprisingcapacity'I 26 yand resistance 2.1 is includedY beltween the anode ofdiodef I8- andthe grid I3- of valve 2, and instead of' a Variable biasbeingI applied to the cathode of diode 24 it is appliedfrom a tappingpointI 28 on- 'a 'potentiometer 23 through resistance 29 to the anodeofdiode- I8, the cathode of diode 24y being connected directly to theanode voltage supply line.- The bias applied'to gridI3 of-valve2 isobtainedfrom across the anode voltage supply. In addition, the backcouplingbetween valves 2 and'3 is obtained by me'ansof a resistance 32'connected between the anode of valve 2 and grid 20, and a ative vafterthe multivibrator comprising Valves 2a and diode 33'is interposedbetweenA the grid'20 and fcapacity22 so asto block'positive pulses butto pass negative pulses which are developed when rectangular masterlpulses are used and are dif- A second multivibrator comprising' valves2a and 3a is connected similarly to'that comprising valves 2 and 3 abovereferred to and is similarly controlled by the masterpulses v appliedvia `capacity 22a, resistance 2|a and diode 33a to grid 20a and isalsocontrolled by anode 'l of valve l via diode |8a, capacity 20a andresistance Zia.

Said multivibrator comprising valves 2a and 3a does not, however,control the voltage of control electrode 9 of valve l because thevoltage applied to the anode of diode l from tapping point 28a:on'potentiometer 23a is's'uch thatsaid multivibrator is triggeredbefore thatcomprising valves 2 and 3 as the voltageofanode T descendsduring the` time when the integrating circuit is oper- As capacity 20amay become charged 3a has'been Ytriggered additional diode-35 islpreferably connected across resistance 27a to `discharge-it before thearrival of the next master pulse; .If it is..desiredrthat either of themultivibrators should be capable of giving a greater delay,then a diodecorresponding to diode 35 'should be connected across the gridresistance 21 and further means, including one or more diodes, should bearranged so that valve is only rendered inoperative and reset when both'multivibrators have been triggered.

.of anode |2a falls following the triggering of multivibratorscomprising valves 2a and 3a. In this way the rate at which the potentialof anode falls will initially be relatively great due to the fact thatin addition to the charging current entering capacity Evia resistance 4,additional charging current is fed into said capacity via resistance 36from a point which is substantially at the anode supply voltage. Afterthe multivibrator comprising valves 2a and 3a has been triggered,however,I resistance 30 is connected to a point of much lowerpotentialand therefore feeds a smaller current to capacity and the rateat which the potential of anode falls becomes much smaller. This may bea useful feature when the ratio of the time delays required is large,for example, of the order of 10:1 or 100:1 and when similar percentageaccuracies in the delay of the pulses are desired.

Although in the arrangements above referred to, one of themultivibrators generating delayed pulses has been employed to render theintegrating device inoperative and to reset it, it will be lappreciatedthat an additional multivibrator may be ebployed solely for the latterpurposes, if desired.

It will also be appreciated that any number of multivibrators may beused to develop delayed pulses providing that it isarranged thatthe'integrating circuit is only rendered inoperative yafter themultivibrator giving the pulse havingthe'greatest delay has beentriggered.

`Further, integrating circuits other than circuits of the kind abovereferred to of the kind described in lthe specification of applicationSerial No. 592,641, led May 8, 1945 may be used, such as, for example, aconventional sawtooth generating circuit in whichv a condenser ischarged exponentially through a resistance from; a source of positivepotential, and discharged by means of a discharging valve in shunt withthe condenser. In this case the integrating circuit is renderedoperative when said discharging valve ceases to conduct, for example,when a suitable negative bias is applied to a control electrode thereof.

The invention may also be applied to the generation of sawtoothwaveforms. One such application of the invention will now be describedwith reference to Figure 3 of the drawings in which valve |0| isemployed in the integrating circuit and valves |02 and |03 are employedin 'the multivibrator circuit. Anode |04 of valve` |01 is connected tothe positive pole of a source of anode voltage |05 through resistance|06 and is also coupled by a feedback capacity |01 to its grid |08,which is connected via charging resistance |09 to the positive pole ofthe source |05 which also provides charging current. Ihis arrangementconstitutes an integrating circuitV asdcscribed in the specification ofcopending application Serial No. 592 641, filed May 8, 1945 in which ascapacity |01 charges, the negative feedback which takesv place viacapacity |01,` causes the voltage of anode |04 to change at a constantrate.

Valves |02 and |03 are connected in a known type of multivibratorcircuit. Their respective cathodes ||0 and are connected together and tothe negative pole of a source of voltage ||2 via a coupling resistanceH3, while the anode A |I4of valve 03 is connected via resistance I5 tothe grid ||6 of valve |02 and is also connected via anode resistance tothe positive pole of the f source of current |05. Grid |B is alsoconnected to the negative pole of source ||2 via resistance I8, and gridI9 of Valve |03 isalso connected to said negative pole via `resistance|20. Anode |2| of valve |02 is connected via resistance |09 to thepositive pole of source |05. As is known, this arrangement has twoconditions of equilibrium in which either valve |02 or valve |03 isconducting and it can be caused from one condition of equilibrium toanother by the change of the bias appliedto the grid of either valve. Inthe present case this control bias is applied to grid ||9 via resistance|22 connected to anode |04, so that as the voltage on anode |04 falls, apoint is eventually reached at which grid H9 becomes suiciently negativeto cause valve |03 to become non-conducting, whereupon saidmultivtbrator circuit changes its condition of equilibrium and valve |02which was formerly non-conducting becomes conducting. Anode |2| of valve02 is connected to grid |08 so that when valve |02 becomes conducting itprovides a path via resistance |3 to the negative pole of source 2through which said capacity |01 may be charged in the opposite sense tovthat in which it is charged by resistance |09. By suitable choice ofthe values of resistance |09 and ||3 and the voltage of sources of |05and ||2, it can be arranged that when valve |02 is conducting, capacity|01 receives a steady increasing:V negativer charge so?, that fthevoltage of anode. |04' will riseat a steady rate. Thus, a point willbe reachedat which the bias of grid ||9 willagainy become sucientlypositivefto cause valve I 03 to conduct, whereupon thermultivibratorwill again change its condition of equilibrium and valve |02' willbecome non-conducting so lthat theintegrating circuit willagain operateas above referred to and the voltage of anodev-|04 will decreasel at asteadyrate. It will therefore be.l seen that a voltage of sawtoothywaveform will bedeveloped across` output terminals T connectedv to anode|04 and cathode of valve |0|.

Figure 4 of the drawings shows a furtheriapplication'of the; inventionto the generation of sawtooth-waveforms: Thecircuit shown in thisfiguresdiifers from thecircuit of Figure 3 only in that aunidirectionally conducting device |23 has beeninterposed ibetween anode|2| and grid |08 and that Valve |02 has been provided with a separateanode resistance |24'. This modication has the advantagethatl anyleakage current which may be passed by valve |02 whenin thenon-conducting.I state no longer passes through the charging resistance|09' due to the fact that the device |23 is so connected that in thesecircumstances it is non-conducting. Thus, the device |23 is convenientlya diode with its cathode connected to anode |22 which is in theVcircumstances referred to positive in relation to vgrid |08 to whichthe anode of diode |23-'is connected. It will be appreciated that incases in which charging resistance |09 has a high value in order tosecure a relatively slow rate of decrease on the 'voltage of anode |04,any leakage1 current flowing through said resistance |09 couldseriouslymodify the slope of the falling portion of the waveform at anode |04.

It will be seen that the arrangements shown in Figures 3 and 4 serve'togenerate sawtooth waveforms and the slopes of the rising andf fallingportions of these waveforms can `hecontroll'ed- -by the choice of valuesof different components in the circuits and the voltages of the.lsources of voltage employed. If desired, the generated'sawtoothv` can besynchronized by means of impulses applied from some external sourceprovided that would normally effect its transition so that thetransition; is causedto-occur by vthe incoming. im.- pulses. Suchcontrol impulses may be confveniently applied through a capacity |25 tovgrid IIB, or if multi-grid, valves, are used instead of triode valvesnshown in the, figures., thesetrigger pulses may be appliedtoothercontrol electrodes, such as suppressor electrodes of suchv valves.

I claim as myinvention:

1. An. electrical circuit arrangement for gen,- erating pulses having apredetermined delaywith respectto amaster pulse comprising anintegrating circuit anda multivibrator circuit having two conditions ofequilibriumv and means for so coupling said circuits that in response tothe voltage or current developed in said integrating circuit reaching apredetermined value, said multivibrator circuitv changes its conditionrof equilibrium and causes an interruption of the integration of saidintegrating` circuit and causes said integrating circuit to be restoredto a predetermined condition, said arrangement having means for applyingsaid master pulse tov said multivibrator'circuit so as to change itscondition of equilibrium to cause said integrating circuit to becomeoperative and a further multivibrator circuit having two conditions ofequilibrium so coupledto said integrating'circuit that when the voltageor current developed in said integrating circuit reaches anotherpredetermined value, said furthermultivibratorcircuit changes itscondition of equilibrium and generates said delayed pulse.

2- The inventionl according to claim 1 wherein there is provided meanscomprising a resistor coupling saidv further multivibrator-'circuit andsaid integrating circuit. for modifying thev rate of said integration asa functionof said. change of the condition of said further multivibratorcircuit.

ERIC LAWRENCE CASLING WHITE.

REFERENCESA CITED The following references are of record ini the le ofthis patent:

UNITED STATES. PATENTS

